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As Apple begins to make preparations for the upcoming iPhone 5S which is widely speculated for Sept. 10, chatter has picked up about the remaining cell phone carriers that Apple has yet to strike a deal. An executive from NTT Docomo, Japan's largest carrier, suggested that a deal between the two companies would make good sense.

In an interview with Japan's
Sankeibiz, NTT Docomo senior executive vice president Kazuto Tsubouchi said an imminent arrival of the iPhone on NTT Docomo's network would be difficult. "It would be difficult to starts sales on the 10th," Tsubouchi said, referring to the rumored imminent launch of the phone.

Shares of NTT Docomo were higher in Monday trading, gaining 1.7% to $16.17. Apple shares were also gaining, tacking on 0.55% to trade at $503.78.

Apple is expected to announce the unveiling of two phones next month. In addition to the iPhone 5S, which will reportedly come in a gold or champagne backing as well as the standard black and white, Apple will also unveil a cheaper iPhone, currently dubbed the iPhone 5C.

Apple declined to comment for this story.

With over 61 million mobile customers in Japan, NTT Docomo is Japan's largest carrier that doesn't sell the iPhone.
SoftBank and
KDDI currently have contracts with Apple, per the company's
carrier support site.

While NTT Docomo pales in comparison to China Mobile and its 760 million mobile subscribers, getting the largest carrier in Japan would be another feather in Apple's hat. Apple owned 35.9% of the Japanese smartphone market as of the end of March, according to a May report from Japan's
MM Research Institute. Trailing Apple are
Fujitsu with 13% and
Sony with 12% of the market.

NTT Docomo has over 15 million subscribers to its Xi (pronounced "crossy") service, which is the company's extra-high-speed LTE mobile service. While Apple will not capture all 15 million subscribers, anything that Apple
does capture is not currently baked into analysts' estimates, and would have to be factored in when building models for fiscal 2014 and beyond.

For fiscal 2014, Apple is expected to generate $180.2 billion in revenue, with much of that coming from the iPhone. In Apple's most recent quarter, the company generated $35.323 billion in revenue, with 56.2% of that coming from the iPhone. It's clear that although Apple has other products, the company is reliant on the iPhone to generate a healthy portion of its revenue.